During the drilling of a well, it is commonplace to process the drilling mud returns to remove undesired drilled cuttings or solids utilizing a shale shaker or the like. The shale shaker is the primary piece of equipment which separates the drilling solids from the mud. It is also desirable to produce a mud with a low drilled solids content. By recycling the large drilled solids in the shale shaker, thin sizes of drilled solids are produced and thereby build up the solids content of the mud. As the solids content increases, the mud must be thinned by adding additional water which necessitates the addition of more weighting material to maintain the mud at its desired weight.
In addition to removing undesired large drilled solids and producing a mud with a low drilled solids content, it is also desirable to recover and recycle drilling fluids and solid particulate material such as copolymer spheres or beads. The beads are usually circulated through the system once and then discarded. It is economically beneficial to recycle these potentially costly beads during the drilling process. It is conventional to screen the mud in a shale shaker having screens ranging in size from 10 to 200 mesh. Thus, any solid particulate materials having a particle size larger than the shale shaker screen would be removed from the system with the drilled solids.
Efforts have been made to deposit the drilled solids and copolymer beads into a tank containing a liquid which has a specific gravity less than that of the drilled solids but greater than that of the copolymer beads or spheres. As a result, the copolymer beads or particulate materials migrate or float to the top of the liquid and can then be skimmed from the upper portion of the vessel and then returned to the well for recirculation. In these systems, the flotation liquid in the tank requires an aqueous solution of sodium carbonate or any number of soluble salts such as sodium chloride or calcium chloride to induce the separation of the beads, liquid and drilled solids. The introduction of the more efficient shale shakers that produce finer solids has made this flotation system ineffective. This flotation system did not anticipate the problem of fine solids building up in the separating fluid zone. As these solids continue to build up, the separating liquid becomes extremely viscous or thick and will not allow the copolymer spheres to be effectively separated from the drilled cuttings. Furthermore, the sodium carbonate on the surface of the copolymer spheres which are returned to the drilling fluid will create a problem for the drilling fluid known as carbonate contamination. Carbonate contamination produces carbonic acid which reacts with the alkaline products in the drilling fluid which in turn reduce the effectiveness of drilling fluid thinners such as lignosulfonates and allow the drilling fluids to become increasingly thick and unacceptable.